By that, I mean, actual teams that played together (for one game/contest/match or more) in a competitive environment with the goal of winning the game/contest/match.

In most cases, it would be things like national teams or all-star teams.

My suggestion for the greatest ice hockey team ever assembled would be the 1987 Canada Cup team from Canada.
I've listed every member of the team, by position, Name, birth place, professional team at the time, and achievements.

HOF = eventually Hall of Fame member
AS = number of all-star game appearances
SC = number of Stanley Cups won
Aw = number of individual NHL awards/trophies won

Interesting exercise. There are some limitations to this, off course, in that the HOF, AS, SC and AW metrics effectively limit the pool of possibly contending teamsup until, say, the early 90's (or even later) to Canadian and American teams (but let's be real, Canadian teams, although at least the American teams get a fair shake by having access to the NHL during that pre-90's period). Would any of the Red Army teams have stacked up? Probably not, but we'll never really know, just like we will never be able to say whether any pre-integration baseball team was the "greatest" ever. Greatest North American team of all time? Sure.

I'd throw the 1992 US men's basketball "dream team" into that mix (sans Christian Laettner, of course.) Jordan, Magic, Bird, Barkley, Ewing, Malone, Drexler, and Robinson were every bit as dominant as they were supposed to be. A quick Wiki check has ten of the twelve members among the NBA's all-time 50 best players.

The Boston Celtics of 1957-1969 I'd think are the creme de la creme of greatest basketball teams- even more so than the Dream Team- and possibly of any sport.

First, it wasn't an Olympic or All-Star equivalent assembled for a short run, but an actual team that played day in and day out. While the exercise allows for shorter-lived Dream Team like creations- and I think you could argue that at the time they were formed, the Dream Team was the greatest basketball team on the planet- I'd argue that "greatness" should also consider longevity. The Dream Team won a single gold medal during a two week run against entirely foreign-born, non-NBA squads, whereas the Celtics of this period played a full season and playoffs against other full fledged every day NBA teams for 13 years.

To that end, over that span of 13 seaons, the Boston Celtics won 11 NBA World Championships, including an unequaled 8 in a row. The two seasons they didn't win it all, they made the Finals in 1958 but lost, and were beaten out in reaching the Finals by Wilt Chamberlain's 76ers squad in 1967.

During that period the Celtics did field numerous Hall of Fame players. Over that 1957-1969 run, they had Bob Cousy, John Havlicek, Tom Heinsohn, Bailey Howell, K.C. Jones, Sam Jones, Frank Ramsey, Bill Russell, and Bill Sharman as future Hall-of-Famers principally known as Celtics players, as well as Clyde Lovelette, Arnie Risen, and Andy Phillip as future HoF members who had short stints on championship clubs during this period. So for the period of this run, the Celtics counted twelve HoF players among their ranks, with as many as eight on the roster at one time in the 1958 season.

Further, of those twelve Hall of Fame players, five were also on the 1996 "50 Greatest Players" list: Bob Cousy, John Havlicek, Sam Jones, Bill Russell, and Bill Sharman. While the Dream Team may have had 10 of the "50 Greatest Players", for an every day team made up through the normal drafting process to boast 4 of those 5 on the floor at the same time, game in and game out (Sharman left in 61, Havlicek joined in 62) over multiple seasons is simply extraordinary.

And not that it necessarily matters, but they were led by arguably the greatest coach in history, Red Auerbach, who retired with the career record in wins (938) and titles (9, since the last two of those 11 went to player-coach Bill Russell). Purely from a social standpoint, he was also pioneering executive who broke the color barrier in the NBA in drafting the first black player, and also went on to assemble the first all-black starting 5 in NBA history.

By that, I mean, actual teams that played together (for one game/contest/match or more) in a competitive environment with the goal of winning the game/contest/match.

Oops, I kind of missed those criteria.

No, yours makes the list. The Eskimos were a legitimate team (not some year end "all-star" team that only plays one game against another "all-star" team, where no one seems to give a damn about the outcome).

As for the basketball one, I think the idea of the 1992 Dream Team playing the 1958 Celtics in a 81 game season would be AWESOME. I would have picked the Dream Team as the best of all time (basketball), but hincandenza presents a very good case for the Celtics being the best ever.

As a challenge to the 1987 Canada Cup squad I suggested, I guess the 1977 Montreal Canadiens (9 HOF players), 1957 Montreal Canadiens (8 HOF players) or 1968 Montreal Canadiens (8 HOF players) would be the equivalent of the dynasty Celtics (in hockey).

On purely number of HOFers, an argument could be made for the 2002 Red Wings. Though most of the marquee players were in their twilights, they boasted no less than 10 current or potential HOFers (Yzerman, Larionov, Hull, Robitaille, Chelios, Hasek, Shanahan, Fedorov, Lidstrom, Datsyuk) and 7 players won medals in the 2002 Olympics. If Jiri Fischer's career wasn't cut so short, they could've had 11 potential HOFers.